Ocean bottom seismic cable recording apparatus

Abstract

An ocean bottom seismic cable recording apparatus comprising a plurality of seismic node casings (1), said node casings being separated from each other by separate stress member sections (2), each stress member section having acoustic decoupling arrangements (3) at each end connecting to said seismic node casings (1), and where each seismic node casing comprising an autonomous sensor capsule (5) for sensing and recording seismic data, and wherein the autonomous sensor capsule (5) is removable from said seismic node casing (1), and wherein each seismic node casing (1) further comprising an inner compartment (4) accommodating the autonomous sensor capsule (5).

Description

INTRODUCTION[0001]The present invention relates to the field of marine seismic exploration. More particularly, the invention relates to an apparatus for marine seismic data acquisition using ocean bottom seismic cables; an ocean bottom seismic cable recording apparatus, a method for deployment of the ocean bottom seismic cable recording apparatus and a method for recovery of an ocean bottom seismic cable recording apparatus.BACKGROUND[0002]Marine seismic exploration is normally conducted by firing a seismic source towed close to the sea surface by a vessel. The seismic energy is propagating down through the earth and parts of the transmitted energy will return to the surface after being reflected and / or refracted by discontinuities in the sub surface. The discontinuities are formed by interfaces between layers having different elastic properties and are called seismic reflectors. The returned energy is recorded by seismic sensors at the sea bottom or near the sea surface. In marine ...

AI Technical Summary

Benefits of technology

This invention is about a new system for recording seismic data in ocean bottom surveys. The system uses individual stress member sections that connect seismic node casings via acoustic decoupling devices. The cable does not contain any electrical or optical wiring, making it stronger and more durable. The system also has a smaller physical size, making it easier to handle and store onboard the vessel when detached from the node casing. The proposed new apparatus is well-suited for conducting ocean bottom seismic surveys at any water depth and offers significant cost savings compared to existing systems.

Problems solved by technology

This type of cable is sensitive to water leakage through its multiple electrical terminations.

Hence, this method has the weakness of being inherently slow since during the deployment and retrieval one has to take into account that the cable is sensitive to any stretch or bending forces.

If the cable suffers from leakage, the cable typically has to be retrieved, repaired and redeployed before the data acquisition can commence.

Data acquisition using this type of ocean bottom cables are relatively costly because of the slow cable handling and since the common practice is to use three vessels, one source vessel, one cable laying vessel and one combined cable laying and recording vessel.

Both these methods are very time consuming and hence expensive.

These types of recording nodes are typically large and heavy.

The cost / sampling issues limit the application of nodes to areas where OBS cable surveys are not an option for operational reasons, for example in the vicinity of infra-structures or in deep water.

However, the cable based systems have limitations when used in deeper waters due to high stress on the cable with its electrical and / or optical wiring as well as an increased probability for water leakage at the electrical terminations between the cable and each sensor house.

It has proven to be difficult to operate large receiver spreads due to the operational difficulties mentioned above.

As a result, much time is spent on shooting overlaps.

In deep waters, cable based systems suffer from an increase in mechanical wear and tear and technical down time to be able to compete with node based systems.

The acquisition methods described above are not viable solutions for larger surveys.

Despite their ability to provide better azimuth and offset coverage as well as S-wave data, the efficiency of these systems are too low compared to surface towed streamer seismic systems.

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